If you have a shell configured in "manage jenkins" and that shell is not available on the slave used by a workflow sh step, then the error does not help you diagnose the issue.

e.g.

node ('different_slave') {
  sh 'echo hello'
}

produces the following error

[workflow_test] Running shell script
sh: 1: /home/jenkins/slave/workspace/workflow_test/.e59a0d2c/script.sh: not found

this implies an error with Jenkins code and not the configuration.

Compare this to the same failure in a FreeStyle Job

[huh] $ c:\cygwin64\bin\bash -xe /tmp/hudson2505861960930827932.sh
FATAL: command execution failed
java.io.IOException: Cannot run program "c:\cygwin64\bin\bash" (in directory "/home/jenkins/slave/workspace/huh"): error=2, No such file or directory

Notice how the FreeStyle is explicit about which shell it is trying to run and what could not be found.